TFT-LCDs have advantages of small size, low power consumption, low radiation, etc. TFT-LCDs developed fast in recent years and can offer better display performance with increase in size of display panel. In TFT-LCDs, a normal white driving mode is always adopted, in which a black image is displayed when a voltage is applied to pixel electrodes and the panel is transparent for light when no voltage is applied.
FIG. 9 is an equivalent circuit diagram of a conventional TFT-LCD. As shown in FIG. 9, when the thin film transistor (TFT) as a switching element of each pixel is turned on, the data signal is transmitted to the pixel electrode of the pixel via the TFT. The voltage applied on the pixel electrode controls the orientation of the liquid crystal molecules in the liquid crystal cell so as to control the light passage. During scanning in one frame, the pixel voltage is maintained through a storage capacitor formed by the pixel electrode and a pixel common electrode line. That is, the pixel voltage is maintained by the storage capacitor (Cst) formed with the pixel common electrode line (Cst on Common). In the operation of the TFT-LCD, the TFTs are turned on in sequence, and data signals are introduced into the pixels in sequence. When the gate line in the nth row is applied with a high voltage (Vgh) and the TFTs in the nth row are turned on, the gate lines in remaining rows are applied with a low voltage signal (Vgl) so that the TFTs in these rows are turned off and the voltage of the pixels in these rows can be maintained with Cst.
FIG. 10 is an equivalent circuit diagram of the design of Cst on Common. A plurality of gate lines 1 and a plurality of data lines 2 intersect with each other to define a plurality of pixels, and each pixel has a pixel electrode 5 formed therein. For each pixel, the gate line, the data line, and the pixel electrode are interconnected with a three-terminal switching element, that is, a pixel TFT 6. A plurality of pixel common electrode lines 4 are provided for forming storage capacitors, and the pixel common electrode lines 4 are parallel to the gate lines 1 and partially overlap with the pixel electrodes 5 in each row. The pixel common electrode lines 4 are directly connected with a common electrode line 3 in the periphery region of the panel. Therefore, in operation, no matter whether the pixel is turned on, a same voltage is applied to the pixel common electrode line for forming the Cst. After the pixel electrode 5 is charged, the voltage applied on the pixel electrode (data) is maintained until the pixel is recharged in the next frame. When the next frame of image is coming, the image data is refreshed based on the current image. That is, after pixels in the nth row have been turned on and before pixels in the (n+1)th row are turned on, the original display information in the pixels in the (n+1)th row cannot be cleared in time, which causes visual residual and tailing of a motion picture. Thus, the conventional TFT-LCD modifies an existing image to display a new one, which causes visual residual and tailing of a motion picture and also renders a response speed and display quality degraded.
In addition, the gate signal applied on the gate line suffers from delay in transmission, which requires that the resistance of the gate line should be within a certain range, i.e., the line width should be controlled within a range. In design, shading strips are provided on a color filter substrate to shelter the gate line and the pixel common electrode line. Therefore, line width influences aperture ratio of a pixel, and in turn aperture ratio directly affects the ratio of light passing the pixel. If the aperture ratio is larger, the ratio of light passing the pixel is higher. Therefore, in the conventional TFT-LCD, increasing the line width of gate line to reduce signal delay on the gate line conflicts with increasing the aperture ratio of the pixel, and a compromise is needed between a large line width and a large aperture ratio.